1. Field of the Invention
The present invention relates to an elastic wave device in which a multilayer film including a piezoelectric thin film is laminated onto a support substrate, and relates to a manufacturing method thereof.
2. Description of the Related Art
Elastic wave devices are widely used in band-pass filters, resonators, and the like. WO 2012/124648 discloses an elastic wave device that uses a piezoelectric single-crystal thin film.
In WO 2012/124648, a high acoustic velocity film, a low acoustic velocity film, and the piezoelectric single-crystal thin film are laminated onto a support substrate in that order from the bottom. An interdigital transducer electrode and a pad electrode electrically connected to the interdigital transducer electrode are formed on the piezoelectric single-crystal thin film. A bump for making an electrical connection to the exterior is bonded onto the pad electrode.
Meanwhile, in an elastic wave device disclosed in WO 2009/075088, an interdigital transducer electrode is formed upon a piezoelectric substrate. A support frame is formed so as to surround the interdigital transducer electrode. A cover member is laminated so as to close off an opening in the upper surface of the support frame. A pad electrode is formed so as to be electrically connected to the interdigital transducer electrode. An under-bump metal layer is formed so as to pass through the support frame and the cover member. The under-bump metal layer is electrically connected to a pad electrode located therebelow. A metal bump is bonded to an upper surface of the under-bump metal layer.
With an elastic wave device that uses a piezoelectric single-crystal thin film such as that disclosed in WO 2012/124648, the piezoelectric single-crystal thin film is thin and can therefore break easily. On the other hand, the metal bump is bonded directly or indirectly onto the pad electrode from above as an external connection terminal. A high pressure is applied to the pad electrode during this bonding. Furthermore, when the elastic wave device is mounted onto a circuit board, the elastic wave device is pressed onto the circuit board from the side where the metal bump is located. There has thus been a problem in that when bonding the bump, during mounting onto the circuit board, or the like, it is easy for the piezoelectric single-crystal thin film to break below the pad electrode, easy for the laminated structure including the piezoelectric single-crystal thin film to peel away, and so on.
Meanwhile, in the case where a piezoelectric single-crystal thin film structure such as that disclosed in WO 2012/124648 is applied in a structure such as that disclosed in WO 2009/075088, a support layer, a cover layer, or the like may contract due to thermal processing or the like during mounting, causing a large amount of stress to act on the piezoelectric single-crystal thin film through the pad electrode. As a result, this structure has also had a problem in that it is easy for the piezoelectric single-crystal thin film to break, easy for the laminated structure including the piezoelectric single-crystal thin film to peel away, and so on.